| Abstract
| - A series of sterically controlled silacycloalkyl or -alkenyl diamido titanium(IV) complexes cySi(NBut)2TiCl2 (3) have been prepared for the purpose of evaluating their steric interactions and effectiveness as ethylene polymerization catalysts.
- The chemistry of titanium complexes stabilized by a series of cyclic silyldiamide ligands(cycl)Si(HNBut)2 (2) derived from the silacycloalkyl unit -(CH2)nSi-, with n = 3, 4, and 5,has been studied. Thus, a variety of spiro-siladiazatitanacyclobutane complexes (cycl)Si(NBut)2TiCl2 (3) has been prepared by the reaction of the dilithium salt of 2 with titaniumtetrachloride. The reaction of 2 with Ti(NMe2)4 in refluxing toluene yields (cycl)Si(NBut)2Ti(NMe2)2 (4), and the product 4 is converted to 3 in a moderate isolated yield by treatmentwith excess Me3SiCl. Dimethyl complexes of the type (cycl)Si(NBut)2TiMe2 (5) were preparedby the reaction of 3 with MeMgBr. Complexes 3 have been characterized by X-raycrystallography. As a result of the formation of the siladiazatitanacyclobutane ring, thetitanium atoms in 3 exhibit distorted-tetrahedral configurations with the two chloride ligands.In addition, the crystallographic results establish that steric interactions between thesilacycloalkyl and tert-butyl groups influence the C(But)−N−Ti angles and, hence, the stericenvironment at titanium. The compounds 3 were further investigated as potential catalystsfor the polymerization of ethylene. While sterically less demanding silacyclobutyl and -pentyldiamide complexes (3a and 3b) exhibit low ethylene polymerization activity (4.0−5.8 kg PEmolcat-1 h-1) in the presence of methylalumoxane, the highly puckered silacyclohexyl diamidecomplex 3c shows better activity (14 kg PE molcat-1 h-1) for ethylene polymerization whenit is activated with MAO.
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